At what distance does a 100 watt lightbulb deliver the same power per unit surface area as a 75 watt lightbulb produces 10 m away from the bulb? (assume both have the same efficiency for converting electrical energy in the circuit into emitted electromagnetic recall that watts = joules/second = power = energy per unit time. assume that the power of the electromagnetic waves spreads uniformly in all directions (i. e. spreads out over the area of a sphere) and use the formula for the surface area of a sphere.